Laser film debonding method

ABSTRACT

A laser-based coating removal method debonds a film from a substrate rather than ablating the film. A laser light is transmitted through a transparent film to an underlying bonding layer for bonding the film to one or more additional films and/or a substrate. The laser light is absorbed at the bonding layer and the transparent film is released. In some embodiments, after the transparent film is released it is able to be physically removed.

RELATED APPLICATIONS

This patent application claims priority under U.S.C. 119(e) of theco-pending U.S. Provisional Patent Application No. 61/929,887, filed onJan. 21, 2014, and entitled “LASER FILM DEBONDING METHOD,” which ishereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention is generally directed to systems and methods oflaser removal of coatings. More specifically, the present invention isdirected to a method of removing a protective film without damaging theunderlying substrate.

BACKGROUND OF THE INVENTION

In the maintenance and possibly manufacturing or rework of aircraftpropellers it is required that certain damaged protective films beremoved and fresh films be applied to refurbish the propellers andreturn them to use. Such rework or repair may also be required for largeturbine blades of wind powered electric generators. Damage to propellersor blades often occurs from normal use such as wear and tear from highspeed impact of rain and ice particles or bird strikes to sand andgravel impact. Some aircraft runways may consist of only a “dirt” stripor a sandy beach. As such, debris can become airborn and flow into thepropeller or blade wash. Propeller damage may also result from militaryconflict or simple maintenance accidents.

A conventional example of an aircraft propeller and coating is that of apainted metal propeller. However, more recently developed highefficiency and light weight propellers are constructed of fiberglass orcarbon fiber composite substrates rather than aluminum alloys. Thesepropellers may have a protective coating other than paint. A possiblecoating may be polyurethane. These coatings may range in thickness froma few thousandths of an inch to many tens of thousands. Polyurethane isa well known material also used to protect hardwood floors in homes.

To maintain the propellers, the damaged protective film first needs tobe removed. This removal presents a formidable practical problem.Conventional methods such as sanding, media blasting, scrapping orchiseling are both time consuming and may cause further damage to theunderlying composite substrate therefore requiring further timeconsuming and expensive substrate repair after the old protective filmis removed. FIG. 1 illustrates an approach to remove a protective filmsuch as paint on metal such as a painted propeller. In this approach,the film is slowly ablated by decomposing the film in multiple passes ofa scanned laser beam of appropriate optical characteristics. Typically,this approach also requires much power.

SUMMARY OF THE INVENTION

A laser-based coating removal method debonds a film from a substraterather than ablating the film. A laser light is transmitted through atransparent film to an underlying bonding layer for bonding the film toone or more additional films and/or a substrate. The laser light isabsorbed at the bonding layer and the transparent film is released. Insome embodiments, after the transparent film is released it is able tobe physically removed.

In one aspect, a method of removing a protective film from a substratecomprises transmitting a laser light through a transparent film to anunderlying bonding layer and absorbing the laser light at the bonding atthe layer, wherein as the laser light is absorbed at the bonding layer,the transparent film is released. After the transparent film isreleased, the released film is able to be physically lifted away fromthe substrate. Particularly, during the method the film remainssubstantially intact and not melted or deformed or decomposed.Additionally, there is no substantial thermal nor structural damage tothe underlying substrate. In some embodiments, the film is polyurethane.In some embodiments, the substrate comprises fiberglass composite orcarbon fiber and epoxy composite or composite foam material. The laserbeam may be scanned in order to substantially clean up or prepare thesubstrate surface for strong adhesion of a new layer of protectivecoating. In some embodiments, the protective film ranges from 0.001inches to 0.300 inches thickness. In some embodiments, the laserwavelength is in the near infrared. In further embodiments, the laserwavelength is 1064 nanometers. In some embodiments, the laser scanningmethod is completed by a machine such as an XY table. In some of theseembodiments, the XY translator table is computer controlled. In someembodiments, the scanning method is manual such that a laser work headis moved by hand by over the work piece. Alternatively, the work headmay be scanned over the work piece by a robot. In some embodiments, thesubstrate comprises a propeller blade, such as, from an aircraft or ahovercraft or a rotor blade such from a helicopter or from a windturbine blade. In some embodiments, the laser is a pulsed Nd:YAG laser.In some embodiments, the laser average power is at least 10 watts. Infurther embodiments, the laser repetition rate is at least 100 persecond. In some embodiments, a laser spot size ranges from 0.1 mm to 10mm diameter.

In a further aspect, a method of removing a protective film from asubstrate comprises transmitting a laser light through a first filmlayer to a second film layer above the substrate and absorbing the laserlight at an adhering interface between the first film layer and thesecond film layer, wherein as the laser light is absorbed at theinterface, the first film and the second film are debonded. In someembodiments, the first film layer and the second film layer comprisepolyurethane. The first film layer remains intact as the first film andthe second film are debonded. In some embodiments, the protective filmlayers range from 0.001 inches to 0.300 inches thickness. In someembodiments, the laser wavelength is in the near infrared. In furtherembodiments, the laser wavelength is 1064 nanometers.

In another aspect, a method of removing one or more protective filmsfrom a substrate comprises transmitting a laser light through one ormore than one transparent films and absorbing the laser light at anadhering interface between a last film above the substrate and a secondto last film, wherein as the laser light is absorbed at the interface,the last film and the second to the last film are debonded. In someembodiments, the last film above the substrate and the second to lastfilm comprise polyurethane. The second to last film remains intact asthe last film and the second to the last film are debonded. In someembodiments, the protective film layers range from 0.001 inches to 0.300inches thickness. In some embodiments, the laser wavelength is in thenear infrared. In further embodiments, the laser wavelength is 1064nanometers.

In still a further aspect, a laser-based coating removal system toremove a coating from a surface comprises a laser source configured toprovide a laser pulse, a laser scanning head coupled to the laser sourceand configured to direct the laser pulse onto a position on the surface,wherein the laser pulse is configured with a wavelength such that thelaser pulse passes through one or more transparent films and to anunderlying bonding layer, and wherein as the laser light is absorbed atthe bonding layer, the one or more transparent films are released. Insome embodiments, the laser scanning head is machine controlled.Alternatively, the laser scanning head is manually controlled such thatthe work head is moved by hand over the work piece. In some embodiments,the coating ranges from 0.001 inches to 0.300 inches thickness. In someembodiments, the laser wavelength is in the near infrared. In someembodiments, the laser wavelength is 1064 nanometers. In someembodiments, the laser comprises a pulsed Nd:YAG laser. In furtherembodiments, the laser average power is at least 10 watts. In someembodiments, the laser repetition rate is at least 100 per second. Infurther embodiments, a laser spot size ranges from 0.1 mm to 10 mmdiameter.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a prior system for removing a protective film from asurface in accordance with some embodiments.

FIGS. 2 and 3 illustrate a system for removing a protective film from asurface in accordance with some embodiments.

FIGS. 4-6 illustrate a method of removing a protective film from asurface in accordance with some embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention are directed to a system and method fordebonding a film from a substrate rather than ablating the film. A laserlight is transmitted through a transparent film to an underlying bondinglayer for bonding the film to one or more additional films and/or asubstrate. The laser light is absorbed at the bonding layer and thetransparent film is released. In some embodiments, after the transparentfilm is released it is able to be physically removed.

Reference will now be made in detail to implementations of a laser-basedcoating removal system and method as illustrated in the accompanyingdrawings. The same reference indicators will be used through thedrawings and the following detailed description to refer to the same orlike parts. In the interest of clarity, not all of the routine featuresof the implementations described herein are shown and described. It willalso be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions be made toachieve the developer's specific goals, such as compliance withapplication and business related constraints, and that these specificgoals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

The present invention takes a unique and efficient approach to filmremoval by de-bonding the film rather than laboriously ablating it. Theremoval of paint by laser method is a typical example of ablating. Inablation, the film is decomposed into simpler components such as carbondioxide and water vapor. Alternatively the film can be rather explodedor pyrolized on a microscopic level—laser spot by laser spot—from thesurface in thin layers as a laser makes pass after pass to, in effect,shave away the film (paint). This process while quite useful is time andenergy consuming. Indeed for thicker films greater than a fewthousandths of an inch “mils” the process can be time consuming takingperhaps minutes or hours per square foot of area while requiring arelatively high powered laser, say, hundreds of watts of average power.

In the case of removing relatively thick films from large propellerswhich may have on the order of 10 sq. ft of area per blade and which mayrange from a few mils to 100 mils thickness, if an ablation method wereused, the process could take many hours or days to complete.

As shown in FIG. 1, a prior art system utilizes a series of laser lightpulses 115 in order to remove a coating 125 from an underlying primer121 and substrate 120. This ablation approach however, requires multiplepasses, excess energy and time.

FIG. 2 illustrates an example of a system for debonding a film from asubstrate rather than slowly ablating it. As shown in FIG. 2, the systemcomprises a laser source 210 that directs a laser pulse 215 to alocation in order to remove a film 223 from a substrate 220. The film223 is substantially translucent which enables the laser light pulse 215to pass through the film 223 and be absorbed by an underlying primerand/or bonding layer 221 on a surface of the substrate 220. In someembodiments, the protective film 223 comprises a coating material suchas polyurethane and the substrate comprises a metal and/or a compositesuch as carbon fiber or fiberglass. The laser light 215 is absorbed atthe underlying primer and/or bonding layer 221 which causes debondingbetween the film 223 and the substrate 220.

The film 223 to be de-bonded from the substrate 220 is substantiallytransparent to the laser light 215 such that the film transmits thephotonic energy to the underlying bonding layer 221. The underlyingbonding layer 221 is then be substantially or at least sufficientlyabsorptive of the laser energy 215 at the laser wavelength.Consequently, when the laser energy 215 is absorbed by the bonding layer221, the bonding molecules then substantially debond or locallydecompose thereby releasing the overlying film 223. Once de-bonded, theoverlying film 223 for the areas exposed to the laser light 215 can thenbe physically lifted away free of any connection to the substrate 220.In some embodiments, only one pass of the laser light 215 is required.In some embodiments, the laser source 210 comprises a computercontrolled XY translator table. However, the laser source 210 is able tocomprise any appropriately desired computer controlled or manuallyoperated laser scanning head.

The bonding layer 221 may be a primer or other adhesive layer betweenthe substrate 220 and the overlying film 223. In some embodiments, it isalso a thin upper layer of the substrate itself as long as the bondinglayer 221 substantially absorbs the laser energy 215. The absorbedenergy breaks the bond locally in a very thin zone while leaving theoverlying film 223 intact and not damaging the substrate 220.

In some embodiments, the laser source 215 is able to transmit a laserlight through a first film layer to a second film layer above thesubstrate in order to debond the first film layer from the second film.As shown in FIG. 3, a laser source 310 directs a laser pulse 315 to alocation in order to remove the first film 327 from the second film 323and the substrate 320.

The first film 327 and/or upper film is substantially translucent whichenables the laser light pulse 315 to pass through the first film 327 andbe absorbed by an underlying primer and/or bonding layer 325 whichprovides an interface between the first film layer 327 and the secondfilm layer 327. The first film layer 327 and the second film layer 323are able to be transparent to the laser light 315 as long as theunderlying primer and/or bonding layer 325 is able to absorb the laserlight 315 energy. For example, as described above, in some embodiments,the first film 327 and the second film 323 comprise a transparentcoating layer such as polyurethane. The laser light 315 is absorbed atthe underlying primer and/or bonding layer 325 which causes debondingbetween the first film 327 and the second film 323. The underlying orsecond film layer 323 does not have to be the substrate 320. When theenergy is absorbed, the bond breaks between the first film 327 and thesecond film 323, thus interlayer debonding is possible above thesubstrate 320.

FIG. 4 illustrates a method of removing a protective film from asubstrate in accordance with the above embodiments. The method begins inthe step 410. In the step 420, a laser light is transmitted through aprotective film to an underlying bonding layer. In some embodiments, theprotective film is a transparent film such as polyurethane. In the step430, the laser light is absorbed at the bonding layer between theprotective film and an underlying substrate. When the laser energy isabsorbed by the bonding layer the bonding molecules then substantiallydebond or locally decompose thereby releasing the overlying film. Oncede-bonded, the overlying film for the areas exposed to the laser lightcan then be physically lifted away free of any connection to thesubstrate. The method ends in the step 440.

As described above, the laser source is able to transmit a laser lightthrough a first film layer to a second film layer above the substrate inorder to debond the first film layer from the second film. FIG. 5illustrates a method of removing a first and/or top coating layer froman underlying second and/or bottom coating layer. The method begins inthe step 510. In the step 520, a laser light is transmitted through afirst film layer and to a second film layer where the light is absorbedat an adhering interface between the first film layer and the secondfilm layer in the step 530. The first film layer and the second filmlayer are able to be transparent to the laser light as long as theunderlying primer and/or bonding layer is able to absorb the laser lightenergy. When the laser energy is absorbed by the adhering interface theadhering molecules then substantially debond or locally decomposethereby releasing the overlying film. Once de-bonded, the overlyingfirst film for the areas exposed to the laser light can then bephysically lifted away free of any connection to second film and thesubstrate. The method ends in the step 540.

Particularly, the laser light source is able to be used to in order toremove one or more than one transparent films from a substrate. Forexample, FIG. 6 illustrates a method of removing one or more than oneprotective layer from a substrate. The method begins in the step 610. Inthe step 620, a laser light is transmitted through one or more than onetransparent films coupled to a substrate. In the step 630, the laserlight is absorbed at an adhering and/or bonding interface between a lastfilm above the substrate and a second to last film. As described above,when the laser energy is absorbed by the bonding layer the bondingmolecules then substantially debond or locally decompose therebyreleasing the overlying film. Once de-bonded, the overlying film for theareas exposed to the laser light can then be physically lifted away freeof any connection to the substrate. The method ends in the step 640.

The key to this laser method is that the film to be de-bonded from asubstrate is substantially transparent to the laser light such that thefilm transmits the photonic energy to the underlying bonding layer. Theunderlying bonding layer must then be substantially or at leastsufficiently absorptive of the laser energy at the laser wavelength.When such laser energy is absorbed by the bonding layer the bondingmolecules then substantially debond or locally decompose therebyreleasing the overlying film. In such a method the overlying film forareas exposed to the laser light can now be physically lifted away freeof any connection to the substrate.

Adjacent areas not exposed to the laser retain their strong bond. Atsuch a boundary line if it is desired to remove the film at the lasertreated areas, the de-bonded film can simply be cut away with a sharptool (knife, scissor, razor blade) such as in the case of a local repairdepot.

In some embodiments, laser light in the near infrared range, such as,approximately 1 micron, or more specifically, 1064 nanometers wavelengthwill substantially transmit through such a coating material aspolyurethane. In some embodiments, a Nd:YAG laser will generate thislight wavelength at high enough power for practical and economicapplication. Good transmission may occur even for thicknessesapproaching 100 mils. The laser light is further able to be absorbed byunderlying layers such as the top epoxy layer in a fiberglass or carbonfiber composite substrate. The absorption produces very localized andinstantaneous heating at the poly and epoxy interface such as to breakthe bond between the two layers. At the same time the laser energydelivered (fluence) is not so large as to heat the poly layer to meltingor flowing and neither overheats nor damages the composite fiberglass orcarbon fiber substrate epoxy or composite matrix. By way of example,such laser treated areas barely reach human body temperature in apractical application. The laser energy is able to de-bond the layerswith no flame hazard and without smoke or the observation of othervapors.

Scanning Methods

In some embodiments, the laser beam may be scanned over the work pieceby a source machine where an “XY” transport table moves a work pieceunder a laser work head as is generally known in the art. Alternatively,the work piece may also be scanned manually by a hand held work head.Particularly, the work piece is able to be scanned using anyappropriately desired method as known in the art.

Interface Clean Up

In some embodiments, the laser system may further be used to clean up avery thin layer of decomposed primer or adhesive layer which mightresult in the formation of a black “soot” that is created by the locallaser heating and adhesive decomposition at the interface. After thefilm (polyurethane) is lifted away from the substrate (essentially inone piece) a very thin black sooty layer may remain on the substrate.The adhesive may be an epoxy compound.

In case it is desired to clean up the substrate prior to applying a newfresh coat of protective film (polyurethane), traditional manual methodssuch as fine sand papering and solvent wipe can be employed. However,the laser may also be used to clean the interface of soot while notcreating sanding debris nor chemical waste. It has been found that thelaser with substantially the same power and beam scanning setting asused in the de-bonding can clean the surface perhaps better than finegrit sandpaper. Notably a thin layer of bonding compound, which may beepoxy, remains and thereby the composite substrate is still covered.

In operation, the system and method for debonding a film from asubstrate is able to quickly remove such films in minutes on a largepropeller blade, consumes relatively little laser energy and does notdamage the substrate. A composite substrate propeller blade ofapproximate 6 foot length with a protective polyurethane film a few milsto 100 mils thick can have its polyurethane coating de-bonded by laserin about 5 minutes while requiring only 300 watts average laser power atthe surface. The method can work with a pulsed laser as low powered as40 watts average power, but the debonding rate will be proportionallyslower. Of course, the instantaneous laser power for a pulsed laser canbe many tens of kilowatts per spot. The pulse duration for each spot isrelatively short, such as 100 nanoseconds by example. Pulse repetitionrate may be 10,000 per second by way of example.

The present invention takes a unique and efficient approach to filmremoval by de-bonding the film rather than laboriously ablating it. Themethod transmits laser light and photonic energy to an underlyingbonding layer coupling a protective film to one or more additionallayers and/or a substrate. When the laser energy is absorbed by thebonding layer the bonding molecules then substantially debond or locallydecompose thereby releasing the overlying film. In such a method theoverlying film for areas exposed to the laser light can now bephysically lifted away free of any connection to the substrate. The filmis quickly removed without damaging the substrates and while consumingrelatively little laser energy. Accordingly, the laser film debondingmethod as described herein has many advantages.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention.

1. A method of removing a protective film from a substrate comprising: a. transmitting a laser light through the protective film to an underlying and separately applied bonding layer, wherein the bonding layer adheres the protective film to the substrate; and b. absorbing the laser light at the bonding at the layer, wherein as the laser light is absorbed at the bonding layer, the protective film is released.
 2. The method of claim 1, wherein the protective film comprises polyurethane.
 3. The method of claim 1, wherein the substrate comprises fiberglass composite or carbon fiber and epoxy composite or composite foam material.
 4. The method of claim 1, wherein the protective film ranges from 0.001 inches to 0.300 inches thickness.
 5. The method of claim 1, wherein the laser wavelength is in the near infrared.
 6. The method of claim 1, wherein the laser wavelength is 1064 nanometers.
 7. The method of claim 1, wherein the laser scanning method is machine controlled.
 8. The method of claim 1, wherein the scanning method is manual such that a laser work head is moved by hand by over the work piece.
 9. The method of claim 1, wherein the laser comprises a pulsed Nd:YAG laser.
 10. The method of claim 1, wherein the laser average power is at least 10 watts.
 11. The method of claim 1, wherein the laser repetition rate is at least 100 per second.
 12. The method of claim 1, wherein a laser spot size ranges from 0.1 mm to 10 mm diameter.
 13. A method of removing a protective film from a substrate comprising: a. transmitting a laser light at a wavelength to transmit through a first protective film layer to a separately applied adhering interface between the first protective film layer and a second protective film layer; and b. absorbing the laser light at the adhering interface between the first film layer and the second film layer, wherein as the laser light is absorbed at the adhering interface, the first film and the second film are debonded.
 14. The method of claim 13, wherein the first film layer and the second film layer comprise polyurethane.
 15. The method of claim 13, wherein the first film layer remains intact as the first film and the second film are debonded.
 16. The method of claim 13, wherein the protective film layers range ranges from 0.001 inches to 0.300 inches thickness.
 17. The method of claim 13, wherein the laser wavelength is in the near infrared.
 18. The method of claim 13, wherein the laser wavelength is 1064 nanometers.
 19. A method of removing one or more protective films from a substrate comprising: a. transmitting a laser light at a wavelength to transmit through one or more than one protective films; and b. absorbing the laser light at a separately applied adhering interface between a last film above the substrate and a second to last film, wherein as the laser light is absorbed at the adhering interface, the last film and the second to the last film are debonded.
 20. The method of claim 19, wherein the last film above the substrate and the second to last film comprise polyurethane.
 21. The method of claim 19, wherein the second to last film remains intact as the last film and the second to the last film are debonded.
 22. The method of claim 19, wherein the protective film ranges from 0.001 inches to 0.300 inches thickness.
 23. The method of claim 19, wherein the laser wavelength is in the near infrared.
 24. The method of claim 19, wherein the laser wavelength is 1064 nanometers.
 25. A laser-based coating removal system to remove a protective film from a surface, the system comprising: a. a laser source configured to provide a laser pulse; b. a laser scanning head coupled to the laser source and configured to direct the laser pulse onto a position on the surface, wherein the laser pulse is configured with a wavelength such that the laser pulse transmits through the protective films to an underlying and separately applied bonding layer, wherein the bonding layer adheres the protective film to the surface, and wherein as the laser light is absorbed at the bonding layer, the one or more protective films are released.
 26. The system of claim 25, wherein the laser scanning head is machine controlled.
 27. The system of claim 25, wherein the laser scanning head is manually controlled such that the work head is moved by hand by over the work piece.
 28. The system of claim 25, wherein the protective film ranges from 0.001 inches to 0.300 inches thickness.
 29. The system of claim 25, wherein the laser wavelength is in the near infrared.
 30. The system of claim 25, wherein the laser wavelength is 1064 nanometers.
 31. The system of claim 25, wherein the laser comprises a pulsed Nd:YAG laser.
 32. The system of claim 25, wherein the laser average power is at least 10 watts.
 33. The system of claim 25, wherein the laser repetition rate is at least 100 per second.
 34. The system of claim 25, wherein a laser spot size ranges from 0.1 mm to 10 mm diameter. 